The present invention relates to light beam phase modulators and more particularly to such modulators for maintaining quadrature phasing between the light beams which are utilized in interferometers.
Modulators for changing the phase of a light beam passing through an optical waveguide are well known to those skilled in the optical arts. One application for such modulators is found in interferometers of the type wherein a physical parameter is sensed by directing light beams through two separate optical waveguides and wherein means is included for maintaining quadrature phasing between those light beams to permit direct readout from only one of the waveguides. In this application, that one optical waveguide is varied in length and refractive index, which adjusts the optical path length. To vary the length of that optical waveguide, a piezoelectric stretcher is commonly utilized which applies stress to that optical waveguide in some proportion with the voltage applied thereto. Characteristically, such stretchers operate at high voltages, which present difficulties when interferometers are operated outside the laboratory environment. Also, a lengthy piece of optical waveguide is wrapped around the piezoelectric material. Such stretchers are somewhat massive when compared with the other components in the interferometer. Furthermore, when the physical parameter is to be sensed in water, the piezoelectric stretcher must be waterproofed with potting material which only adds further bulk to the interferometer.